Presently, there is a high demand for efficient power converters that address the power needs of commercial products such as computers and cell phones. As a result, multiple different isolated power converter topologies have been developed to meet this ever increasing demand such as flyback, half-bridge and full-bridge converters. Further, to address power factor correction (PFC) concerns while still isolating the main power supply from the output, the prior art has progressed toward numerous “two-stage” power converters wherein the first stage includes a non-isolated boost converter and the second stage includes an isolated converter such as the flyback, half-bridge and full-bridge converters. This is primarily because boost and half-bridge converters have a common ground with the controller IC, and therefore a simple way to close the feedback loop. However, these “two-stage” power converters have the drawbacks of increased design complexity, decreased energy conversion efficiency, increased component counts, increased printed circuit board (PCB) size, and therefore increased cost.
A block diagram of a prior art regulated power apparatus 100 is shown in FIG. 1. The apparatus 100 is a two stage boost half-bridge power converter. The apparatus 100 generally includes an input filter 102, a rectifier 104, a two stage converter 106 including a boost converter 116 (first stage) and a half bridge converter 114 (second stage), a transformer 108, an output filter 110 and a feedback control 112.
The input filter 102 is coupled to receive an AC input signal Vin and to filter out electromagnetic and radio frequency interference/noise. The input filter 102 outputs a filtered AC signal to the rectifier 104. Upon receiving the signal, the rectifier 104 generates an unregulated direct current (DC) voltage and outputs that unregulated DC voltage to the coupled input of the boost converter 116. Typically, the boost converter 116 receives the unregulated DC voltage from the rectifier 104 and generates a boosted or increased voltage. This increased voltage is a regulated DC voltage that is greater than the input unregulated DC voltage. It should be noted that it is well known in the art that unregulated voltage is voltage that is allowed to vary with changes in the load of the circuit and/or changes in the power source voltage. Correspondingly, it is also well known in the art that regulated voltage is voltage that is controlled such that a sufficiently constant output voltage is maintained despite load and/or power source variation. The half bridge converter 114 receives the increased regulated voltage and generates a converted DC signal that is ideally a square wave signal that is output across the inputs to the transformer 108. The transformer 108 converts the DC square wave to a desired output voltage depending on the turn ratio of the transformer 108. Often the desired output voltage is 5, 12 or 24V. The AC voltage signal output from the transformer 108 is input to an output filter 110, which filters out harmonic noise due to the power circuit 100 and converts the AC signal to DC. The DC voltage signal Vout is output to an electrical device (not shown) and a feedback control 112. The feedback control 112 senses a power change in the DC voltage signal Vout and controls a duty cycle of a regulation switching element within the boost converter 116 to supply a compensating power to correct the power change in the DC voltage signal Vout.
One disadvantage of this type of power system is that due to regulations requiring isolation of the main power supply and powered electrical devices, the power apparatus includes an isolating transformer. This results in increased design complexity, increased component counts, increased PCB size, and therefore increased cost.